This invention relates generally to spot-knocking electron tubes and particularly to a system and method for monitoring the spot-knocking of cathode ray tubes (CRT's).
The various electrodes for the electron guns in vacuum tubes, such as cathode ray tubes (CRT'S), typically are made by stamping, shearing and coining processes. The electrodes, therefore, frequently have various surface imperfections, such as burrs. In the assembled electron guns the electrodes are closely spaced. During tube operation each electrode is biased at a different voltage and high voltage differences, as high as 35 kilovolts, therefore are present on the closely spaced electrodes. Under such conditions, the burrs, or other surface imperfections, substantially reduce the spacing between the electrodes and the high voltage difference causes sparking across the burrs and the adjacent electrode. A well known method of removing the undesirable such burrs is a process called spot-knocking. In this process the highest voltage potential electrode, typically the anode, is voltage biased to a very high potential, such as 35 to 40 kilovolts, while the other electrodes are maintained at ground potential. Beneficial sparking is induced by increasing the anode voltage to a level higher than the normal operating voltage. The increase is accomplished by pulsing the anode with an increased voltage, or by applying a radio frequency (rf) component. The combined high potentials cause high voltage discharges, or arcing between the surface imperfections and the electrodes to substantially remove the imperfections.
Typically in the spot-knocking process, the tubes being processed are placed in hangers which move along a conveyor, and which apply the anode potential to the electron guns. Carts, which apply the rf component, move beneath the tubes at the same speed as the conveyor. It is therefore, very difficult to assure that spot-knocking is proceeding in the desired manner because of the inability to observe the tubes during the spot-knocking process. For these reasons it is very difficult to detect improper spot-knocking, which can be caused either by problems within the tube being spot-knocked, or by faulty anode power supplies, or hangers, or rf carts.
For these reasons there is a need for a system and method for automatically monitoring the rf spot-knocking of electron guns within vacuum tubes. The present invention fulfills this need.